The present invention relates to antenna systems and more specifically to multi-beam antenna communication systems.
Pre-distortion networks are known in the art to improve the self-interference or carrier to interference (C/I) ratio of amplifiers. Multi-beam antenna (MBA) arrays also are well known in the art. The power in the sidelobes of beams in a multi-beam antenna array which are operating at the same frequency as an intended signal interfere with the intended signal. This interference limits the proximity of co-frequency beams. There is also interference which is attributable to adjacent frequency channels, albeit typically at a lower intensity, and it is referred to therefore as adjacent channel interference. Interference from adjacent channels limits the proximity of beams on channels operating at adjacent frequencies. Utilization studies show that in typical applications, the C/I ratio caused by the sidelobes is the largest source of self-interference.
In the transmit mode, the signal received by any particular remote user is the sum of the intended signal for that remote user, which is contained in a beam pointing towards that remote user, and the signals intended for other remote users, which interfere with the intended signal. These interfering signals reach the remote user through the sidelobes of beams pointing towards other remote users. In the receive mode, each beam of the receive antenna collects a signal from at least one remote user and the sidelobes of each beam collect signals from other remote users which act as interference to the intended signal in the beam.
What is needed is an interference cancellation network for a multi-beam antenna to permit more capacity to be focussed into high user density regions.
In the present invention, a network is disclosed for increasing the beam traffic capacity of a multi-beam antenna system. The multi-beam antenna system comprises a plurality of signals at any frequency transmitted when the multi-beam antenna is used as a transmit antenna, and signals at any frequency received when the multi-beam antenna is used as a receive antenna, the multi-beam antenna of the multi-beam antenna system transmitting in the transmit mode and receiving in the receive mode a plurality of beams having at least one sidelobe causing interference with at least one of the plurality of signals. The plurality of beams having at least one sidelobe cause interference with at least one of the plurality of signals therein defining at least one antenna sidelobe. The multi-beam antenna system comprises an interference cancellation means for canceling the interference with at least one signal caused by the at least one antenna sidelobe.
In particular, the network increases the beam traffic capacity in a region around any remote user, the size of the region being on the order of 3 to 5 beam widths in any direction from the remote user.
When the multi-beam antenna is used as a transmit antenna, and at least one of the plurality of beams transmitted by the multi-beam antenna is pointed towards at least one remote user, the interference cancellation means has an input port for each of the plurality of signals, the interference cancellation means creates a plurality of composite signals, and the interference cancellation means has an output port for each of the composite signals. The transmit antenna has an input port connected to each output port of the interference cancellation means such that the composite signals become the input signals to the transmit multi-beam antenna, and the composite signals emerging from the interference cancellation means optimize the signal to interference ratio at the at least one remote user.
When the multi-beam antenna is used as a receive antenna, each beam of the receive antenna collects a signal, referred to as the intended signal, from at least one remote user, the sidelobe of at least one beam collecting at least one signal from at least one other remote user, and the signal from the at least one other remote user causes interference to the intended signal in the beam. The receive antenna has for each beam an output port which is connected to an input port of the interference cancellation means such that both the intended signal and the interference emerging from each output port of the receive multi-beam antenna are injected into the interference cancellation means at the input port.
The interference cancellation means creates a plurality of composite signals. The interference cancellation means has an output port for each of the composite signals, and the composite signals emerging from the output port of the interference cancellation means optimize the signal to interference ratio of the at least one intended signal collected from the at least one remote user.
Specifically, when the interference cancellation means is a network in a transmit multi-beam antenna system, the interference cancellation means comprises a plurality of power dividers and a plurality of power combiners. Each power divider has an input port connected to the transmit signal intended to be transmitted by the transmit multi-beam antenna system, and each power divider divides the signal connected to the input port into one reference fractional signal and at least one non-reference fractional signal, therein defining the power divider as a source power divider to the one reference fractional signal and to the at least one non-reference fractional signal. The source power divider has a plurality of output ports, and an output port of the source power divider containing the reference fractional signal is connected to an input port of one of the power combiners, therein defining the power combiner as a companion power combiner to the source power divider. Each output port of the source power divider containing a non-reference fractional signal is connected to an input port of another one of the power combiners, therein defining the another one of the power combiners as an associated power combiner to the source power divider. Each companion power combiner receives the at least one non-reference fractional signal through a path connecting from the source power divider of the at least one non-reference fractional signal, therein defining the source power divider of the at least one non-reference fractional signal as an associated power divider to the companion power combiner. Each of the companion power combiners combine the reference fractional signal emerging from the companion source power divider with the at least one non-reference fractional signal from an associated power divider into a composite output signal, wherein an output port of each of the power combiners is connected to an input port of the transmit multi-beam antenna such that the composite signals emerging from the interference cancellation means at the output ports of each of the power combiners become the signals transmitted at any frequency when the multi-beam antenna is used as a transmit antenna.
Again specifically, when the interference cancellation means is a network in a receive multi-beam antenna system, the interference cancellation means comprises a plurality of power dividers and a plurality of power combiners. Each power divider has an input port connected to an output port of the receive multi-beam antenna, such that the signals at any frequency received when the multi-beam antenna is used as a receive antenna become the input signals to the interference cancellation network. Each of the power dividers divide the signal connected to the input port into one reference fractional signal and at least one non-reference fractional signal, therein defining the power divider as a source power divider to the one reference fractional signal and to the at least one non-reference fractional signal. The source power divider has a plurality of output ports, and an output port of the source power divider containing the reference fractional signal is connected to an input port of one of the power combiners, therein defining the power combiner as a companion power combiner to the source power divider. Each output port of the source power divider containing a non-reference fractional signal is connected to an input port of another one of the power combiners, therein defining the another one of the power combiners as an associated power combiner to the source power divider. Each companion power combiner receives the at least one non-reference fractional signal through a path connecting from the source power divider of the at least one non-reference fractional signal, therein defining the source power divider of the at least one non-reference fractional signal as an associated power divider to the companion power combiner. Each of the companion power combiners combines the reference fractional signal emerging from the companion source power divider with the at least one non-reference fractional signal from an associated power divider into a composite output signal. A composite output signal emerges from an output port of each power combiner of the interference cancellation network, and each output port of each of the power combiners of the interference cancellation network is an output port of the receive multi-beam antenna system, such that the composite output signal of the interference cancellation network is an output signal of the receive multi-beam antenna system
In any case, the multi-beam antenna can be an active phased array antenna or a reflector class antenna with multiple feeds, particularly wherein either each of the multiple feeds are independent and they each create one beam or the feeds are combined in clusters to create beams. Also, the dividing means can comprise a reciprocal combining means or the combining means can comprise a reciprocal dividing means.
In most cases, attenuating means are included for attenuating the amplitude of at least one of the non-reference fractional signals to achieve the desired amplitude relative to at least one of the reference fractional signals. As well, attenuating means can be included for attenuating the amplitude of the reference fractional signal.
Again in most cases, phase shifting means are included for shifting the phase of at least one of the plurality of non-reference fractional signals to achieve the desired phase relative to at least one of the reference fractional signals. As well, phase shifting means can be included for shifting the phase of the reference fractional signal.
The attenuating means can be included with one of the (a) combining means, and (b) dividing means. Similarly, the phase shifting means can be included with one of the (a) combining means, and (b) dividing means.
The present invention also discloses a method for increasing the beam traffic capacity of a multi-beam antenna transmitting a plurality of beams operating at any frequency, with at least one of the plurality of beams pointed toward a remote user, and at least one other of the plurality of beams having at least one sidelobe directed towards the remote user causing interference at the remote user with the signal contained in the beam pointed toward the remote user. The method is performed by means of the interference cancellation network discussed previously, which has as input a plurality of transmit signals each intended to correspond to one of the plurality of beams operating at any frequency. The interference cancellation network comprises a plurality of dividers and a plurality of combiners, with each of the plurality of dividers having a companion combiner and at least one associated combiner, and each of the plurality of combiners having a companion divider and at least one associated divider, and each of the dividers having an input port for one of the plurality of transmit signals. The method comprises the steps of: (a) applying each of the plurality of transmit signals to the input ports of each of the dividers, (b) dividing in each of the dividers each of the transmit signals into a reference fractional signal and at least one non-reference fractional signal, the reference fractional signal and the non-reference fractional signal therein each having a common source divider, (c) transporting the reference fractional signal to the companion combiner of the common source divider, (d) transporting at least one non-reference fractional signal to one of the at least one associated combiners of the common source divider, and (e) combining in each of the companion combiners the one reference fractional signal from the companion divider with the at least one non-reference fractional signal from the at least one associated divider into a composite signal, the composite signal thereby optimizing the signal to interference ratio at the remote user.
The present invention discloses a method for increasing the beam traffic capacity of a multi-beam antenna receiving a plurality of beams operating at any frequency, the multi-beam antenna having a receive signal output port for each of the plurality of beams operating at any frequency, with at least one of the plurality of beams collecting an intended signal from at least one remote user, the at least one of the plurality of beams having at least one sidelobe collecting at least one signal from at least one other remote user, and the at least one signal from the at least one other remote user acting as interference to the intended signal emerging from the output port of the multi-beam receive antenna associated with the at least one beam collecting an intended signal from the at least one remote user. The method is again performed by means of the interference cancellation network previously discussed, which has as input a plurality of receive signals emerging from the output ports of the receive multi-beam antenna. The interference cancellation network comprises a plurality of dividers and a plurality of combiners, each of the plurality of dividers has a companion combiner and at least one associated combiner, each of the plurality of combiners has a companion divider and at least one associated divider, and each of the dividers has an input port for one of the output receive signals corresponding to one of the plurality of beams received by the multi-beam antenna. The method comprises the steps of: (a) applying each of the receive signals emerging from the output ports of the receive multi-beam antenna to the input ports of each of the dividers, (b) dividing in each of the dividers each of the receive signals into a reference fractional signal and at least one non-reference fractional signal, the reference fractional signal and the non-reference fractional signal therein each having a common source divider, (c) transporting the reference fractional signal to the companion combiner of the common source divider, (d) transporting the at least one non-reference fractional signal to one of the at least one associated combiners of the common source divider, and (e) combining in each of the companion combiners the one reference fractional signal from the companion divider with the at least one non-reference fractional signal from the at least one associated divider into a composite signal, the composite signal thereby optimizing the signal to interference ratio of the intended signal collected from the at least one remote user.
For either the transmit mode or the receive mode, the method in most cases includes, following the step of dividing in each of the dividers each of the signals into a reference fractional signal and at least one non-reference fractional signal, the step of attenuating the amplitude of the at least one of the plurality of non-reference fractional signals to achieve the desired amplitude relative to at least one of the reference fractional signals. Also, in most cases, following the step of dividing in each of the dividers each of the signals into a reference fractional signal and at least one non-reference fractional signal, the method includes the step of shifting the phase of the at least one of the plurality of non-reference fractional signals to achieve the desired phase relative to the phase of at least one of the reference fractional signals.
The method can be applied to a multi-beam antenna which is an active phased array antenna. Also, the method can be applied to a multi-beam antenna which is a reflector class antenna with multiple feeds, particularly wherein either each of the multiple feeds are independent and they each create one beam or the feeds are combined in clusters to create beams. In particular, the method increases the beam traffic capacity in a region around any remote user, the size of the region being on the order of 3 to 5 beam widths in any direction from the remote user.